Fuel injection systems based on common rail technology provide important advantages to engine and vehicle manufacturers who are under continual pressure by environmental regulatory bodies to reduce the pollution caused by the engine whilst improving the performance of the vehicle offered to the end user.
Principally, common rail technology enables the amount of fuel delivered to the combustion cylinders of the engine to be controlled precisely whilst providing high pressure injection and flexible injection timing. Important advantages are thus gained in terms of fuel economy and emissions. However, in order to operate efficiently, it is important that the pressure of fuel within the common rail is controlled accurately to a desired pressure level despite any disturbances that may be caused to the system.
In use, the relationship between the fuel pressure within the common rail (hereafter ‘rail pressure’) in response to the amount of fuel pumped into the common rail by a high pressure supply pump is that of a dynamic system. Typically, therefore, the high pressure fuel pump is controlled by a combination of open-loop and closed-loop control in order to fulfil the functional requirements of i) maintaining the desired rail pressure during changes of injection quantity, ii) varying the rail pressure in response to a change in pressure demand quickly and accurately, and iii) being resilient to system disturbances such as changes in fuel viscosity due to variations in temperature and fuel grade.
A typical fuel system comprises an accumulator volume in the form of a common rail which supplies fuel under high pressure to a plurality of fuel injectors. Fuel is supplied to the common rail from a high pressure rail supply pump, in the form of a number of unit pumps. Each unit pump comprises a pumping chamber within which fuel is pressurised by a pumping plunger. The plunger is driven in a reciprocating motion by a cam arrangement. The unit pumps are supplied with relatively low pressure fuel from a transfer pump.
Seizure of any of the unit pumps will affect the performance of the fuel system and consequently will affect the performance of the vehicle. Following seizure of a unit pump an engine may need to be shut down or run in a reduced mode of operation to prevent damage occurring to engine components. It is therefore highly desirable to be able to detect the seizure of a unit pump, e.g. because the pumping plunger has seized.
Known systems of detecting anomalous engine behaviour (e.g. U.S. Pat. No. 6,076,504 or EP1036923) operate by detecting a deviation from normal engine behaviour. Such systems represent fairly basic methods of detecting anomalous behaviour and generally only return an indication that there is some type of atypical engine condition. Specific information relating to the type of failure is not detectable under such systems.
It is therefore an object of the present invention to provide a detection apparatus for detecting anomalous behaviour within the fuel system.